I can see having a character dedicated to these buffs as a good plan, but I don't understand why you can't re-new it right away. From what I've seen in the game you can't cast Barrier/MBarrier/Wall/Big Guard as long as you still have these buffs... unless you are wasting MP. Even if its low and you want to cast it then instead of now. If you have a protect status running out you have to wait until its allllll gone before your dedicated buffer is allowed to do its job.